1. Field of the Invention
This invention relates to vacuum mixing apparatus especially useful for mixing dental cements, liners, bases, composite restoratives, sealants and bone augmentation materials.
2. Description of the Related Art
The efficacy of mechanical mixing of dental materials such as restoratives is, in general, well recognized to those versed in the art. Handling and strength properties of mechanically mixed materials are improved by virtue of a more complete dispersion of the ingredients or components in one another. Since a large number of dental offices are provided with dental triturators or amalgamators, it is consequently efficient and convenient for the practitioner to use such mixing apparatus for combining ingredients other than amalgams.
For example, mechanically mixed pastes formed from powder and liquid components are typically characterized as exhibiting a greater fluidity and somewhat lower visual opacity than the same pastes prepared by hand mixing or spatulation. Mechanical mixing of a liquid and powder, when compared to hand mixing, normally results in a more thorough wetting of the powder particles which reduces air space between adjacent particles and improves consolidation of the paste.
In addition, the effective working time or placement time of mechanically mixed reactive materials is greater than the working time of hand spatulated materials since the time required for mechanical mixing is significantly shorter than the time normally required for mixing the ingredients by hand. Mechanical mixing also provides added convenience, mix reliability and reproducibility and saves considerable time.
Recently, efforts have been directed toward improving the aesthetic qualities of light curable ionomer restoratives. It has been found that the translucency and surface smoothness of such restoratives can be improved by mechanically mixing the ingredients under vacuum to remove opacifying air bubbles and voids. During one study, vacuum mixing of resin composites was found to reduce porosity in the material by about 90 percent and increase the diametral tensile strength by 11.5 percent. For the dentist or dental assistant, such a reduction in porosity facilitates the establishment of polishable, smooth surfaces on the restorative with improved resistance to staining, and the number of potential plaque propagation sites is correspondingly reduced. Moreover, a reduction in opacity leads to a greater depth of cure and an improved cosmetic appearance.
However, conventional vacuum mixing apparatus is not entirely satisfactory when used in dental offices. Conventional apparatus is often provided with a vacuum hose which must be manually connected to the mixing container before the mixing operation, and then disconnected from the container in order to facilitate access to the mixed materials, and such a procedure is somewhat time consuming. In addition, the expense of apparatus dedicated to vacuum mixing is not an insignificant sum.